The purpose of this research is to continue to improve our understanding of dental pain by determining sensory nerve location in teeth, axonal transport dynamics of dental nerve endings, and ultrastructure of those nerve endings and their junctions with odontoblasts and other pulpal cells. Such structural information is important if we are to understand the sensory mechanisms of teeth and thereby develop improved management of dental pain. The following studies are proposed: (1) Autoradiographic mapping to finish determining the location and branching patterns of mesencephalic and gasserian trigeminal nerve endings in monkey and rat teeth, and to determine whether that location correlates with sites of greatest occlusal stress. (2) Continued electron microscopic studies of nerve endings in extracted human teeth and in axonal transport labeled teeth of monkeys and rats, using special stains to enhance membrane ultrastructure; the nerveodontoblast associations in normal crowns will be compared with those in reparative dentin, root dentin, or under coronal cavity preparations. (3) Comparative ultrastructural studies of sensory receptors in periodontium, in order to define the unique features of the receptors in pulp and dentin as compared to those structues common to all the receptors. (4) Structure/Function correlations in developing, aging, denervated and reinnervated rat molars in order to determine the structures essential for normal function; a new method for analyzing sensitivity of rat molars will be used that measures the digaatric muscle reflex response to graded electrical stimulation of molar teeth. These studies will lead to improved understanding of dental sensory mechanisms, and, since teeth primarily sense pain, to improved understanding of pain receptor structure and function.